1. Field of the Invention
The present invention relates to the structure of a flexible sheet-like bent actuator constituted by a multi-layer structure such as a bimorph or unimorph structure capable of being fabricated easily and permitting complicated and large movements, as well as a method of manufacturing the same.
2. Description of the Related Art
Actuators adapted to generate force and displacement in accordance with an electric signal are presently in use in various industrial fields and the required performances tend to become more and more diversified. For example, actuators used in the fields of precision machines and industrial robots are required to generate a large force and be quick in response and accurately controlled in position. On the other hand, in the case of an active catheter for medical use and rehabilitation equipment, it is required for them to be small-sized, light-weight, soft, low in driving voltage and capable of being handled safely. Further, in the case of a mobile type tactile display or a pin display as a concave/convex display, a thin, light-weight actuator matrix of a large area is needed for operating a pin matrix. Such a thin and light-weight actuator matrix is needed not only for the pin matrix but also in various fields including next generation type free-running small-sized robots and conveying systems utilizing a ciliary movement.
As such a thin and light-weight actuator permitting a matrix configuration, an actuator whose material itself can be deformed repeatedly in accordance with electric signals is more suitable than an actuator which requires assembly of parts such as an electromagnetic motor. As presently well-known examples of the actuator whose material itself is deformed repeatedly, there are mentioned a piezo-actuator which utilizes the piezo effect of ferroelectric and an SMA actuator which utilizes the phase transition of a shape-memory alloy (SMA).
As an actuator which is still lighter and capable of being formed as a thin film, an organic actuator using an organic material adapted to be deformed with an electric signal is now attracting attention of many concerns. Since the organic actuator uses an organic material, not only it is light-weight, but also the material can be easily formed into a sheet shape. Thus, the organic actuator is applicable to a thin and light-weight actuator. However, among such organic actuators, those low in driving voltage and capable of being handled safely have so far operated mainly in only solutions and thus their application fields have been limited.
Recently, however, organic actuators able to operate in gaseous phase, e.g., in the atmosphere, have been reported. Examples of such actuators include an actuator which utilizes deformation at the time of desorption of molecules caused by heat of a conductive polymer (Japanese Patent No. 3131180) and an actuator comprising a carbon nanotube, an involatile ionic liquid and a polymer (Japanese Patent Laid-Open Publication No. 2005-176428).
The present inventors have developed and disclosed an actuator constituted by a composite material comprising conductive particles and a polymer as a new organic actuator which operates in gaseous phase, e.g., in the atmosphere, (Mitori KATO and Masayoshi ISHIBASHI, “New Polymer-Actuators Using Carbon Nano-particle Composite (II)” 23rd Annual Conference of the Robotics Society of Japan, 2005, 1A32). This organic actuator uses an organic composite material which has been made highly electrically conductive by mixing a binder polymer with conductive particles, and voltage is applied to the organic composite material to generate Joule heat, then movement of deformation of the actuator is performed by utilizing a reversible thermal expansion cased by the self-heat generation.
This organic actuator, in comparison with other organic actuators, uses a material less expensive and easy to be improved and can perform a stable operation without influenced by the environment.
In such a thin actuator, like a thin actuator which utilizes the difference in thermal expansion coefficients between metals in order to enlarge the amount of deformation, it is advantageous to laminate materials different in the amount of deformation relative to a temperature and thereby effect a bending motion, like a bimorph structure or a unimorph structure.
The organic actuator described in the foregoing Japanese patent 3131180, which utilizes a thermal expansion and which is constituted by a composite material containing conductive particles, is easy to handle because it is deformed with an electric signal in gaseous phase (atmosphere) and can be formed easily into a sheet shape or the like. Therefore, it is suitable for application to a thin actuator of a laminate structure such as a unimorph structure.
[Patent Literature 1]
Japanese Patent No. 3131180
[Patent Literature 2]
Japanese Patent Laid-Open Publication No. 2005-176428
[Non-Patent Literature 1]
Mitori KATO and Masayoshi ISHIBASHI, “New Polymer-Actuators Using Carbon Nano-particle Composite (II),” 23rd Annual Conference of the Robotics Society of Japan, 2005, 1A32